JNK2 contains a specificity-determining region responsible for efficient c-Jun binding and phosphorylation

Area of Science:

• Molecular Biology
• Cell Signaling
• Enzymology

Background:

• c-Jun transcriptional activity is regulated by phosphorylation mediated by c-Jun amino-terminal kinases (JNKs).
• Cells express two JNK forms (46-kD and 55-kD), but their specific roles and substrate recognition mechanisms for c-Jun remain unclear.
• JNK1, a 46-kD MAP kinase, has been identified, but the 55-kD JNK form's identity and function require further elucidation.

Purpose of the Study:

• To identify and characterize the 55-kD JNK form.
• To investigate the differential binding affinities and substrate recognition mechanisms of JNK1 and JNK2 towards c-Jun.
• To elucidate the structural basis for the observed differences in JNK-c-Jun interaction.

Main Methods:

• Molecular cloning of the 55-kD JNK form (JNK2).
• Comparative analysis of JNK1 and JNK2 identity, regulation, and binding kinetics with c-Jun.
• Structural investigation using modeling to identify key interaction regions.

Main Results:

• The 55-kD JNK was cloned as JNK2, showing 83% identity and similar regulation to JNK1.
• JNK2 exhibited approximately 25-fold higher binding efficiency and a lower Km for c-Jun compared to JNK1.
• A beta-strand-like region near JNK2's catalytic pocket was identified as crucial for enhanced c-Jun binding, likely acting as a docking site.

Conclusions:

• JNK1 and JNK2, despite close similarity, possess distinct substrate recognition capabilities for c-Jun.
• A specific structural feature in JNK2 facilitates efficient c-Jun interaction, explaining differential biological responses mediated by related MAP kinases.
• Understanding these molecular mechanisms is key to deciphering complex signaling pathways.